The present invention relates to a method of forming a bipolar transistor, and more particularly to a method of forming a polycide emitter electrode in a bipolar transistor.
A polycide emitter electrode of a bipolar transistor comprises a double layered structure of a polysilicon layer and a refractory metal layer overlying the polysilicon layer. The refractory metal layer is deposited on the polysilicon layer by a sputtering method after a natural oxide film is removed by a surface treatment using a fluorine acid solution. This conventional surface treatment causes the following problems. The natural oxide film non-uniformly resides over the polysilicon layer, and then the refractory metal layer is deposited on the non-uniformly residual natural oxide film over the polysilicon layer. This non-uniformly residual natural oxide film on the interface between the refractory metal layer and the polysilicon layer causes the resistance of the emitter to increase or vary, thereby make it difficult to obtain stable performances of the bipolar transistor.
In order to solve the above problem, it was proposed to carry out a radio frequency plasma etching process using argon ions at a high acceleration energy for removing the natural oxide film on the polysilicon layer. The radio frequency plasma etching process, however, raises another problem. If a radio frequency power is high, argon ions are implanted into the polysilicon layer, whereby a damage is provided to the surface of the polysilicon layer, resulting in a rough and damaged surface of the polysilicon layer. The implanted argon in the polysilicon layer is gasified by a post heat treatment process for forming the bipolar transistor to generate argon gas. This argon gas generation causes the refractory metal layer to be peeled from the polysilicon layer and also causes an expansion of the refractory metal layer. The peeling and expansion of the refractory metal layer cause drop of the manufacturing yield of the bipolar transistor and also causes the variation of the emitter resistance. The variation of the emitter resistance results in variation in performance and characteristics of the bipolar transistor.
In the above circumstances, it had been required to develop a novel method of forming an emitter electrode of a bipolar transistor free from the above problem.
Accordingly, it is an object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor free from the above problems.
It is a further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor allowing a high manufacturing yield.
It is a still further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor having a uniform emitter resistance.
It is yet a further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor having uniform performances and characteristics.
It is yet a further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor free from any argon gas generation in a post-heat treatment for forming the bipolar transistor.
It is yet a further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor free from any peeling of the refractory metal layer from the polysilicon layer due to an argon gas generation in a post-heat treatment for forming the bipolar transistor.
It is yet a further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor free from any expansion of the refractory metal layer due to an argon gas generation in a post-heat treatment for forming the bipolar transistor.
It is yet a further object of the present invention to provide a novel method of forming an emitter electrode of a bipolar transistor, wherein an interface of a refractory metal layer and a polysilicon layer is free of any damage.
It is another object of the present invention to provide a novel method of forming an electrode of a semiconductor device free from the above problems.
It is a further object of the present invention to provide a novel method of forming an electrode of a semiconductor device allowing a high manufacturing yield.
It is a still further object of the present invention to provide a novel method of forming an electrode of a semiconductor device having a uniform emitter resistance.
It is yet a further object of the present invention to provide a novel method of forming an electrode of a semiconductor device having uniform performances and characteristics.
It is yet a further object of the present invention to provide a novel method of forming an electrode of a semiconductor device free from any argon gas generation in a post-heat treatment for forming the bipolar transistor.
It is yet a further object of the present invention to provide a novel method of forming an electrode of a semiconductor device free from any peeling of the refractory metal layer from the polysilicon layer due to an argon gas generation in a post-heat treatment for forming the bipolar transistor.
It is yet a further object of the present invention to provide a novel method of forming an electrode of a semiconductor device free from any expansion of the refractory metal layer due to an argon gas generation in a post-heat treatment for forming the bipolar transistor.
It is yet a further object of the present invention to provide a novel method of forming an electrode of a semiconductor device, wherein an interface of a refractory metal layer and a polysilicon layer is free of any damage.
The present invention provides a method of forming an emitter electrode of a bipolar transistor, the emitter electrode comprising a double-layered structure of a polysilicon layer and a refractory metal silicide layer. The method comprises the steps of: removing a natural oxide film from a surface of a polysilicon layer by a sputter-etching process using inert gas ions in the range of acceleration energy from 5 eV to 50 eV; depositing a refractory metal layer on the surface of the polysilicon layer; and carrying out a heat treatment to cause a silicidation reaction to form a refractory metal silicide layer over the polysilicon layer.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.